Remediation Technologies - Environmental Investigation and Remediation - page 326

Air sparging Grade

Vapor extraction

Vault

In well air-stripping

VOC vapor phase

Mounded
groundwater
from sparging
and extraction

Cleaner,
low-density water

Negative
gradient

Negative
gradient

Dissolved
oxygen

Dissolved
oxygen

Pump

FIGURE 7.1 Various removal processes simultaneously applied in the ART In-Well System. (From Odah,
M.M., Powell, R., and Riddle, D.J., 2005, Remediation Journal 15(3): 51-64.)

90% removal. The fact that 1,4-dioxane levels in extracted vapors were as high as g/m 3 demon-

strated that removal in the vapor phase was a signii cant mechanism. Chlorinated VOC removal
rates were predictably high as well. The results of this pilot study with a single well led the state to
approve the ART In-Well technology as the primary remediation method for the site.

μ

7.1.3 P ERVAPORATION
An additional vaporization technique for the separation of contaminants from water, generally in
industrial applications, is referred to as pervaporation. This process is a combination of evaporation
and membrane permeation, which uses relatively low temperatures and pressures for cost-effective
ex situ separation of liquids with similar boiling points. In the pervaporation process, the membrane
is gas permeable, which allows VOCs in the gas phase to pass through the membrane, while water
is prevented from passing ( Figure 7.2 ). Chemicals in a mixture can be separated from each other
because their partial pressures and membrane permeabilities differ. Pervaporation effectively sepa-
rates azeotropic mixtures, which have similar boiling points and evaporation rates.
Specii c studies related to separation of 1,4-dioxane from water have been performed by using a
variety of innovative pervaporation membranes to increase l ux rates, separation efi ciency, or resis-
tance to chemical and thermal degradation. Pintauro and Jian (1995) assessed the capability of sepa-
ration of 1,4-dioxane from water with a polyvinylidene l uoride resin membrane. Their results
indicated that pervaporation separation of 1,4-dioxane from an aqueous solution did occur, but at
signii cantly lower rates than for other contaminants, such as benzene, toluene, or chloroform.
Flux rates through the membrane, at percent-level concentrations of 1,4-dioxane, were on the
order of 5 g/(m 2 h).